The present invention relates to a liquid crystal light control element, a lens barrel, and an imaging device.
The imaging device, such as digital camera and video camera, is provided with a lens barrel containing an optical system to lead the object image, an imaging device (such as CCD) aligned with the optical axis of the optical system, and a light control means for regulating the amount of light led to the imaging device, said light control means crosses the optical axis of the optical system.
The light control means is usually an iris diaphragm which mechanically adjusts the aperture. The iris diaphragm suffers the disadvantage of requiring iris blades and a mechanism to drive iris blades, which occupy a large space in the lens barrel. Therefore, the iris diaphragm is unfavorable to the size reduction of the lens barrel.
To tackle this problem, there has been proposed an imaging device provided with a liquid crystal light control element which does not need a large space. Japanese Patent Laid-open No. 2002-82358.
The conventional liquid crystal light control element, which is indicated by a reference numeral 16 in FIG. 4, has only one liquid crystal layer, which is indicated by a reference numeral 1614 in FIG. 4. The liquid crystal layer 1614 consists of a large number of rod-like liquid crystal molecules 1625, which are hermetically sealed in a container such that they incline while keeping their long axes parallel to each other. The angle of inclination (with respect to the thickness direction of the liquid crystal layer) varies in proportion to the voltage applied to the light control element 16.
The liquid crystal molecules 1615 permit more light to pass through as the angle of orientation of their long axes decreases with respect to the passage of light, resulting in an increased light transmittance. By contrast, the liquid crystal molecules 1615 permit less light to pass through as the angle of orientation of their long axes increases with respect to the passage of light, resulting in a decreased light transmittance.
The conventional light control element 16 with only one liquid crystal layer 1614 is limited in the amount of light that can be regulated. In other words, it is incapable of adequately regulating the amount of light to be led to the imaging device in an ambience with a plenty of light.